TAMPA, Fla. (CBS Local) — 145 coffins have been detected on the grounds of a Florida high school, which once was the site of an African-American cemetery.

Ground-penetrating radar located the caskets on the campus of C. Leon King High School in Tampa, Hillsborough County School Board officials announced on Wednesday.

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The coffins are buried three to five feet deep in about an acre of open land near a small building used by school’s agricultural program, the district said.

Officials believe the caskets were part of Ridgewood Cemetery, a pauper’s burial ground from the mid-20th century that was sold to the school district as part of the property where King High School was later built and opened in 1960.

Records indicate the site could hold the remains of more than 250 people, nearly all of whom were African American, the school district said.

Officials began investigating last month after cemetery researcher Ray Reed tipped a school board member of the possible location of the cemetery.

“It’s shown just how ugly things were here even through the 1950s,” Reed told CBS affiliate WTSP. “And not just at the person level, but with our institutions as well.”

The county Medical Examiner and the State Archaeologist are expected to review the district’s findings in the next 30 days. The agencies can keep possession of the land or turn it back to the school district, officials said.

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The predominately African American cemetery is the second to be discovered this year. In September, residents of an apartment complex in Tampa were forced to move after learning they had been living at the site of Zion Cemetery.